The sexual partnering of young women with older men in Zimbabwe is the "major behavioral determinant" of the higher HIV prevalence among young women compared to young men, according to a study published in the June 1 issue of the ^Lancet. ~

Simon Gregson of the department of infectious disease epidemiology at Imperial College in London and colleagues used survey data from 4,429 young men and women in Zimbabwe's Manicaland province that looked at their sexual histories and sexual practices between July 1998 and January 2000. The young men and women were then screened for HIV and pregnancy.

Women between the ages of 15 and 24 were "considerably more likely" than men in the same age group to be HIV-positive. The prevalence of HIV infection among women of this age group began rising around age 16 and remained "extremely high" through the early 20s.

In contrast, rises in HIV prevalence among men were generally not seen until the mid- to late-20s and early 30s. Median age at first sexual experience was comparable for both men and women, with earlier age at first experience and higher overall number of lifetime partners being associated with increased HIV risk for both sexes.

The researchers theorized that young women are more likely to become infected with HIV because they tend to partner with men who are five to 10 years older than themselves who have had more exposure to the virus, while young men tend to partner with women of similar ages. An analysis of the responses of sexually experienced survey participants determined their hypothesis to be correct, with age difference between partners being a significant predictor of HIV status (odds ratio 1.04).

An Explanation

In Zimbabwe, it is culturally acceptable for women to marry young, while men are encouraged to find employment and accumulate wealth before marrying in their late 20s or early 30s.

Therefore, women are encouraged to pair with older, more established men. Young women who participated in the survey listed "attract[ing] a husband" and marriage among their top reasons for having sex. Some young women also are encouraged by family members to have sex as a way of winning favors or gifts from men.

In relationships between younger women and older men, condoms are rarely used because the men are "making an economic investment in the relationship, wish to avoid extra expense and feel there is less need because young women are free of HIV," the authors state.

Young women often do not insist on condom use because they fear that they may "lose economic benefits" and in some cases are seeking to become pregnant to force a man into marriage, they add. Young women seem more likely to insist on condom use with younger partners "whose bargaining position is weaker and who wish to avoid pregnancy and marriage" themselves.

Changing Behavior

The partnering of younger women with older men plays a "pivotal role in the persistence of major HIV epidemics," not only because many women are infected through these relationships, but because "many further infections result when these women marry and have children," the authors state.

These partnerships "provide far greater exposure to HIV" because sex is "more frequent, condom use is rare and their partners ... are more likely to be infected." They are also more likely to have other concurrent partners.

The authors state that "[b]reaking this link in the pattern of transmission must become a central focus of HIV prevention strategies." They admit that it is "unrealistic to expect to alter the underlying socioeconomic context quickly," but note that "understanding its nature and influence on local patterns of sexual behavior should aid development of more relevant and, therefore, more effective HIV prevention strategies."

They add that raising awareness of the higher prevalence of HIV among young people should encourage condom use among singles and could increase HIV testing and counseling among couples considering marriage.